1. Statement of the Technical Field
The inventive arrangements relate to ultrasonic piezomotors, and more particularly to ultrasonic piezomotors having high rotational speed and torque.
2. Description of the Related Art
Ultrasonic piezomotors are well known in the art. Such motors work on the principal of excitation of ultrasonic standing wave(s) within a piezoelectric resonator. An ultrasonic piezomotor includes a piezoelectric ring resonator and pushers formed of metal or some other material. The pushers can be attached to the piezoresonator directly or through a wave shell. An ultrasonic radial standing wave is excited in the piezoelectric resonator causing the ring to expand and contract in radial direction, stimulating movement of the pushers along the radius. Such a device is commonly excited at the zero order radial mode of vibration of the annular piezoelement, which is considered most effective in terms of amplitude and the quality factor (Q factor) of the whole system.
Because of their elasticity, the pushers vibrate with the same frequency, although phase shifted, in a direction orthogonal to the radius of the ring. The superposition of the two orthogonal movements results in elliptical movements of the pushers. Because the pushers are held pressed against the rotor, their movement, via friction at the pusher contact area, causes rotation of the rotor.
Ultrasonic piezomotors as described herein offer unique properties of very high angular resolution and fast response. Such motors can also provide relatively high torque. However the maximum speed of rotation of a high-torque ultrasonic piezomotor is generally limited.